Audit fixes

certora/Ngt.spec

@@ -292,102 +292,6 @@ rule approve_revert(address spender, uint256 value) {
     assert lastReverted => revert1, "Revert rules are not covering all the cases";
 }
 
-// Verify correct storage changes for non reverting increaseAllowance
-rule increaseAllowance(address spender, uint256 value) {
-    env e;
-
-    address anyUsr;
-    address anyUsr2; address anyUsr3;
-    require anyUsr2 != e.msg.sender || anyUsr3 != spender;
-
-    mathint wardsBefore = wards(anyUsr);
-    mathint totalSupplyBefore = totalSupply();
-    mathint balanceOfBefore = balanceOf(anyUsr);
-    mathint allowanceSenderSpenderBefore = allowance(e.msg.sender, spender);
-    mathint allowanceOtherBefore = allowance(anyUsr2, anyUsr3);
-    mathint noncesBefore = nonces(anyUsr);
-
-    increaseAllowance(e, spender, value);
-
-    mathint wardsAfter = wards(anyUsr);
-    mathint totalSupplyAfter = totalSupply();
-    mathint balanceOfAfter = balanceOf(anyUsr);
-    mathint allowanceSenderSpenderAfter = allowance(e.msg.sender, spender);
-    mathint allowanceOtherAfter = allowance(anyUsr2, anyUsr3);
-    mathint noncesAfter = nonces(anyUsr);
-
-    assert wardsAfter == wardsBefore, "increaseAllowance did not keep unchanged wards";
-    assert totalSupplyAfter == totalSupplyBefore, "increaseAllowance did not keep unchanged totalSupply";
-    assert balanceOfAfter == balanceOfBefore, "increaseAllowance did not keep unchanged every balanceOf[x]";
-    assert allowanceSenderSpenderAfter == allowanceSenderSpenderBefore + value, "increaseAllowance did not increase allowance[sender][spender] by value";
-    assert allowanceOtherAfter == allowanceOtherBefore, "increaseAllowance did not keep unchanged the rest of allowance[x][y]";
-    assert noncesAfter == noncesBefore, "increaseAllowance did not keep unchanged every nonces[x]";
-}
-
-// Verify revert rules on increaseAllowance
-rule increaseAllowance_revert(address spender, uint256 value) {
-    env e;
-
-    mathint allowanceSenderSpender = allowance(e.msg.sender, spender);
-
-    increaseAllowance@withrevert(e, spender, value);
-
-    bool revert1 = e.msg.value > 0;
-    bool revert2 = allowanceSenderSpender + value > max_uint256;
-
-    assert revert1 => lastReverted, "revert1 failed";
-    assert revert2 => lastReverted, "revert2 failed";
-    assert lastReverted => revert1 || revert2, "Revert rules are not covering all the cases";
-}
-
-// Verify correct storage changes for non reverting decreaseAllowance
-rule decreaseAllowance(address spender, uint256 value) {
-    env e;
-
-    address anyUsr;
-    address anyUsr2; address anyUsr3;
-    require anyUsr2 != e.msg.sender || anyUsr3 != spender;
-
-    mathint wardsBefore = wards(anyUsr);
-    mathint totalSupplyBefore = totalSupply();
-    mathint balanceOfBefore = balanceOf(anyUsr);
-    mathint allowanceSenderSpenderBefore = allowance(e.msg.sender, spender);
-    mathint allowanceOtherBefore = allowance(anyUsr2, anyUsr3);
-    mathint noncesBefore = nonces(anyUsr);
-
-    decreaseAllowance(e, spender, value);
-
-    mathint wardsAfter = wards(anyUsr);
-    mathint totalSupplyAfter = totalSupply();
-    mathint balanceOfAfter = balanceOf(anyUsr);
-    mathint allowanceSenderSpenderAfter = allowance(e.msg.sender, spender);
-    mathint allowanceOtherAfter = allowance(anyUsr2, anyUsr3);
-    mathint noncesAfter = nonces(anyUsr);
-
-    assert wardsAfter == wardsBefore, "decreaseAllowance did not keep unchanged wards";
-    assert totalSupplyAfter == totalSupplyBefore, "decreaseAllowance did not keep unchanged totalSupply";
-    assert balanceOfAfter == balanceOfBefore, "decreaseAllowance did not keep unchanged every balanceOf[x]";
-    assert allowanceSenderSpenderAfter == allowanceSenderSpenderBefore - value, "decreaseAllowance did not decrease allowance[sender][spender] by value";
-    assert allowanceOtherAfter == allowanceOtherBefore, "decreaseAllowance did not keep unchanged the rest of allowance[x][y]";
-    assert noncesAfter == noncesBefore, "decreaseAllowance did not keep unchanged every nonces[x]";
-}
-
-// Verify revert rules on decreaseAllowance
-rule decreaseAllowance_revert(address spender, uint256 value) {
-    env e;
-
-    mathint allowanceSenderSpender = allowance(e.msg.sender, spender);
-
-    decreaseAllowance@withrevert(e, spender, value);
-
-    bool revert1 = e.msg.value > 0;
-    bool revert2 = allowanceSenderSpender - value < 0;
-
-    assert revert1 => lastReverted, "revert1 failed";
-    assert revert2 => lastReverted, "revert2 failed";
-    assert lastReverted => revert1 || revert2, "Revert rules are not covering all the cases";
-}
-
 // Verify correct storage changes for non reverting mint
 rule mint(address to, uint256 value) {
     env e;

src/Ngt.sol

@@ -100,7 +100,7 @@ contract Ngt {
 
         unchecked {
             balanceOf[msg.sender] = balance - value;
-            balanceOf[to] += value;
+            balanceOf[to] += value; // note: we don't need an overflow check here b/c sum of all balances == totalSupply
         }
 
         emit Transfer(msg.sender, to, value);
@@ -126,7 +126,7 @@ contract Ngt {
 
         unchecked {
             balanceOf[from] = balance - value;
-            balanceOf[to] += value;
+            balanceOf[to] += value; // note: we don't need an overflow check here b/c sum of all balances == totalSupply
         }
 
         emit Transfer(from, to, value);
@@ -142,28 +142,6 @@ contract Ngt {
         return true;
     }
 
-    function increaseAllowance(address spender, uint256 addedValue) external returns (bool) {
-        uint256 newValue = allowance[msg.sender][spender] + addedValue;
-        allowance[msg.sender][spender] = newValue;
-
-        emit Approval(msg.sender, spender, newValue);
-
-        return true;
-    }
-
-    function decreaseAllowance(address spender, uint256 subtractedValue) external returns (bool) {
-        uint256 allowed = allowance[msg.sender][spender];
-        require(allowed >= subtractedValue, "Ngt/insufficient-allowance");
-        unchecked{
-            allowed = allowed - subtractedValue;
-        }
-        allowance[msg.sender][spender] = allowed;
-
-        emit Approval(msg.sender, spender, allowed);
-
-        return true;
-    }
-
     // --- Mint/Burn ---
     function mint(address to, uint256 value) external auth {
         require(to != address(0) && to != address(this), "Ngt/invalid-address");
@@ -203,7 +181,7 @@ contract Ngt {
         address signer,
         bytes32 digest,
         bytes memory signature
-    ) internal view returns (bool) {
+    ) internal view returns (bool valid) {
         if (signature.length == 65) {
             bytes32 r;
             bytes32 s;
@@ -218,12 +196,14 @@ contract Ngt {
             }
         }
 
-        (bool success, bytes memory result) = signer.staticcall(
-            abi.encodeWithSelector(IERC1271.isValidSignature.selector, digest, signature)
-        );
-        return (success &&
-            result.length == 32 &&
-            abi.decode(result, (bytes4)) == IERC1271.isValidSignature.selector);
+        if (signer.code.length > 0) {
+            (bool success, bytes memory result) = signer.staticcall(
+                abi.encodeCall(IERC1271.isValidSignature, (digest, signature))
+            );
+            valid = (success &&
+                result.length == 32 &&
+                abi.decode(result, (bytes4)) == IERC1271.isValidSignature.selector);
+        }
     }
 
     function permit(